This invention relates to self-standing containers or bags and more particularly to a self-standing bag made of a blank in the form of film or sheet, which is heat-fused along at least two lateral edges thereof. The invention also relates to method and apparatus for automatically producing this self-standing bag.
Ordinarily, the blank from which conventional bags are to be produced, is made of basic sheet or foil of synthetic resin or metal. A film of paper, metal, polyester, nylon, or the like material, which is not heat-fusible, is coated on the surface of the basic sheet expected to become the outer surface of the bag, and a film of easily heat-fusible or heat-sealable synthetic resin such as polyethylene is coated on the other surface of the basis sheet to be brought into the inner surface of the bag when it is completed. Between the basic sheet and either one of the above described films, an intermediate layer of a suitable nature may be interposed if required.
For the production of a conventional bag, the blank is first cut into a configuration conforming to the developed shape of the bag. The blank thus cut into the above described configuration is then folded along a line conforming to the bottom line, and the lateral edges of the folded blank are heat-fused. However, the bag simply heat-fused along its lateral edges cannot stand by itself when it is filled with a content. In order to obviate this disadvantage, there has been proposed a bag with a bottom wall sheet of a substantial area for providing the bag with self-standing ability when it is filled with a content.
One example of such a self-standing bag is disclosed in Japanese Patent Publication No. 9704/1965. The bag disclosed therein comprises first and second side wall sheets of identical shape and size disposed in an opposing relation, and a separate bottom wall sheet which is folded along its centerline into a inverted V-shaped cross-section. The bottom wall sheet is interposed between the lower parts of the first and second side wall sheets, and the lower edges of the inverted V-shaped bottom wall sheet are heat-fused with the lower edges of the first and second side wall sheets.
Each of the three wall sheets of this known bag is made of sheet material with a heat-fusible film attached to the inner surface thereof and with a non-heat-fusible film on the outer surface thereof.
Thus, when the lateral side edges of the first and the second side wall sheets are subjected to heat-fusing operations all of the directly opposing surface of the lateral side edges of the side wall sheets are heat-fused and joined except in regions thereof where the lateral side edges of the bottom wall sheet are interposed.
In this known bag, a cutout or notch is further provided in each lateral side edge of the bottom wall sheet. Therefore, along the lower part of each lateral side edge of the bag produced, a first region wherein the two side wall sheets are directly fused together and a second region wherein the two side wall sheets are indirectly heat-fused with the intermediary of the double-folded edge of the bottom wall sheet are alternately formed because of the existence of the cutout, and an abrupt change in thickness occurs at transitional area between the first and second regions.
In this transitional area, insufficient fusing tends to occur, and since this area is exposed to the outside, the heat-fused structure therein tends to be broken easily.
Furthermore, because this bag requires the three wall sheets as starting blanks, means for supplying three separate blanks is required in manufacturing the bag. It is apparent that this makes the production of the bag complicated and costly.